1. Field of the Invention
The present invention relates to an oil holding cylinder for use in an oil coating roller of a fixing device employed in an electrostatic copying machine, an electrophotographic printer, or the like.
2. Description of the Related Art
Most of fixing devices employed in electrostatic copying machines, electrophotographic printers and similar devices have parts called oil coating rollers. When rotating in contact with a fixing roller, this oil coating roller applies a very small amount of silicone oil to the fixing roller so as to improve the separation property of a recording paper. In addition, at the same time, the oil coating roller wipes up toner adhering to the fixing roller so as to prevent offset from occurring.
In some cases silicone oil, with which a fixing roller is coated by means of an oil coating roller, is supplied successively to the oil coating roller from an oil reservoir member provided separately. However, usually a constant amount of silicone oil is held in the oil coating roller itself, and the entire oil coating roller is exchanged for a new oiling coating roller when the oil held therein has been used up.
Although there are various mechanisms for holding silicone oil in an oil coating roller, a system which can hold enough oil to enable the oil coating roller to be used for a long time is characterized by having a core shaft which is made oil-permeable and has a hollow portion, with silicone oil enclosed or charged in the hollow portion. In this system, the enclosed oil is exuded onto the surface of the hollow core shaft gradually, and the exuded oil is distributed, by capillary action, over an oil coating roller surface layer made from felt of heat-resistant fiber. As the oil-permeable hollow core shaft, that which is provided with a number of small-diameter holes in a metal pipe (see JP-U-59-73762, JP-U-60-110854, JP-A-60-136782), that which is made of porous sintered metal (see JP-A-60-247276), and so on have been used.
An oil coating roller using such a conventional oil-permeable hollow core shaft has been disadvantageous in that the quantity of coating oil exuded from the surface varies largely in use of the oil coating roller. Further, the quantity of coating oil can become excessive to thereby stain a recording paper with oil, particularly when the oil coating roller is reused after the oil coating roller has not been used for a long time.